The invention relates to a device for removing dross from steel slabs.
The present invention relates to an apparatus and method for removing dross ridges from the bottom of steel slabs.
In the production of steel by the continuous casting process, the continuous cast length of steel emerging from the caster is cut into slabs to form separate rectangular flat bottomed pieces. The slabs are conveyed from the cutting operation to storage or further processing by means of computer controlled, motor powered, horizontal, parallel, spaced apart rollers, which are capable of moving the slab in a forward or reverse direction. The produced slabs are then subjected to subsequent processing, as by rolling, to form a finished steel product.
The cutting operation to produce slabs as described above is conventionally performed by means of an oxygen torch, wherein a jet of high purity oxygen is directed against the work piece while it is heated to the oxygen ignition temperature. The resulting exothermic chemical reaction between the iron and oxygen produces slag or waste, which consists of iron oxide, metallic iron and other alloy elements. This slag or waste is in the molten state, and it is displaced during the cutting operation and a portion thereof forms a ridge of the material along the lower edge of the cut end. Upon cooling, the waste solidifies and adheres to the slab along the bottom surface adjacent to the cut end, and forms what is commonly called a xe2x80x9cdross ridge.xe2x80x9d
The formation of the dross ridges on the slabs presents problems in the further processing of the slab. For example, a dross ridge may drop off in the reheat furnace, which requires that it then be removed, thus involving additional labor. Also, in the event that the dross ridge remains adhered to the slab during reheating, it is laminated into the steel during rolling, resulting in an inferior product.
The dross ridges resulting from the torch cutting operation have been removed by a process involving inverting the slab and removing the dross ridges with scarfing torches. However, this process required additional handling of the slab and necessitated additional equipment and labor. Mechanical chippers or chisels have been employed for this purpose, but this also is a labor-intensive process.
More recently, there has been introduced to the art devices that are inserted into the line of rollers conveying the dross containing slab. These devices contain chisel edge cutting blades that sit beneath the slabs. The slab is passed over blades that cut the dross. The cutting blades pivot on a shaft, using a motor or a hydraulic cylinder and levers. Other schemes using cutting blades have been proposed. These cutting devices are used with dross disposal chutes that funnel the dross into receiving bins immediately after removal. In the case of large slabs, the dross removed is in the form of elongated strips that rapidly fill the disposal chutes and receiving bins and, unless frequently removed, can jam the roller line or damage the dross removing apparatus.
The prior art devices as described above all use chiseled edge or other configured dross removal blades. In the case of chiseled edge blades, the first irregularity present in the dross causes the sharp edge of the blade to dig into the metal and rotate upward. This results in more steel being removed than necessary. Also, in a short time the blades become dull and require sharpening.
It would be an advance in the art to provide an improved dross cutting apparatus that minimized cutting of good steel while simultaneously removing the dross. Additionally, it would not employ metal gouging sharp edged blades. Also another improvement would be to cut the dross into smaller pieces while it is removed from slabs to increase bin storage capacity. Further, it would be an advantage to accurately position the means for leveling the device horizontally, and holding the apparatus stationary between dross removal cycles and a lock to prevent the turning of the apparatus during servicing and maintenance.
The invention comprises an apparatus for removing dross from the bottom front and back edges of torch cut slabs of continuous cast steel being conveyed upon a line of rollers. The slabs treated by the apparatus of the invention are flat bottomed and are substantially free from warping or other defects. The apparatus comprises at least one blade support mounted upon a motor driven rotatable spindle. This spindle is horizontally positioned below and between two adjacent slab-conveying rollers. The spindle is journaled in bearings and is mounted at an interior angle of about 6xc2x0-15xc2x0 from the parallel lines of the slab conveying rollers. Preferably, the angle is 10xc2x0-15xc2x0 between and below two of the line rollers. It also has a pair of opposed parallel dross removing blades having their back edges mounted upon the blade support. Preferably, the tops of the blades have an approximately 10xc2x0 downwardly sloped area. Their front edges have a surface that is approximately 90xc2x0, e.g., 0xc2x0 plus or minus 2xc2x0 from the sloped area on top. Upon rotation of the blade support from the horizontal position, the downwardly sloped flat top is brought into horizontal contact with the bottom of a slab. The blade holders and the blades are slightly longer than the width of the slab from which the dross is removed. There is at least one vertical dross cutting blade mounted on the blade support at an angle perpendicular to the line of rollers and extending beyond the vertical end of the dross removing blades. The top of this dross cutting blade is machined to be flush with and have the same contour as the dross removing blades.
Also provided is a power source for rotating the spindle. The device can be operated using existing computerized control means employed to control the line of rollers or a dedicated computerized control of its own. Due to the angled position of the apparatus, the dross removing blades are positioned so that the vertical ends shave the dross from the ends of the slabs as a continuous sliver or strip. The computerized control means are programmed to rotate the spindle sufficiently to remove any dross that has fallen on top of the apparatus.
The apparatus has a horizontal leveling mechanism for insuring that the blade support is secure between dross removal cycles. This leveling mechanism is comprised of a vertical disk having a front face and a top and is attached to the spindle between the power source and its bearing. The front face contains a frustro conical horizontal opening that extends partially through the width of the vertical disk. There is also provided a horizontally positioned movable pin having a frustro conical end sized and positioned to engage the frustro conical horizontal opening in the front face in response to a signal from the control means. There are two vertical holes extending partially into the top and the bottom of the vertical disk. These holes are positioned to correspond to the horizontal position of the blade support. They are designed to mate with a stationary hole located above the spindle. Also provided is a manually withdrawable locking pin for engaging the holes in the top of the vertical disk and the stationary hole.
In a preferred embodiment, the invention comprises a pair of blade supports, desirably rectangular in configuration, mounted back to back on gussets attached to the rotatable horizontally positioned spindle. The blade supports at their ends contain a pair of opposed, parallel, spaced apart dross removing blades, having the back edges mounted upon the blade supports. The dross removing blades are preferably made of two or more sections. Each dross cutting blade is comprised of a vertical blade permanently attached to a flat plate in an inverted xe2x80x9cTxe2x80x9d configuration. This configuration fits into a slot formed between two adjacent sections of the dross removal blades.
In most instances, the control means rotates the dross removing blades about 10xc2x0 to position their flat top in contact the bottom of the slab. It also positions the blade so that the vertical ends shave the dross from end to end of the slabs as they move on the line of rollers. The control means also rotate the blade supports sufficiently at least 180xc2x0 to remove any dross that has fallen thereon. Desirably, the front face of the disk contains a pair of opposed frustro conical horizontal openings. These openings mate with a movable horizontally positioned pin having a frustro conical end sized to engage the frustro conical openings in the front face in response to a signal from the control means.
The preferred power source is a hydraulic motor or geared hydraulic motor or electric motor or geared electric motor for rotating the spindle. The existing computer control means or dedicated control means are known to the art as Process Logic Control computers. They are used in most continuous casting operations and are well known and may be programmed to perform a variety of functions. In this invention, the Process Logic Control computer is programmed for rotating and horizontally positioning the dross removing blades. The computer also rotates the blade supports so that the flat top of the dross removal blade contacts the bottom of the slab and is positioned so that the vertical end shaves the dross from end to end of the slabs as they move on the line of rollers. The computer also signals the rotation of the spindle sufficiently to remove any dross that has fallen thereon.
To provide for the accurate horizontal positioning of the blade supports and to prevent rolling of the apparatus so that it will not accidentally strike a slab being or about to be processed, there are provided speed and directional control valves for hydraulic power sources or reversible variable speed control means for electrical power sources. Also utilized is one set of three vertical raised bands located on the side of the vertical disk in the 90xc2x0 position as measured from the horizontal position of the blade supports. These vertical bands provide input to two sets of three stacked proximity position limit switches. These limit switch sets are located adjacent to each other on opposite sides of the vertical disk. They accurately control the speed and directional control devices to provide rotational slowdown, for either clockwise or counter clockwise rotation of the blade supports just prior to reaching the horizontal position.
The invention further contemplates a method of removing dross from the bottom front and back edges of torch cut slabs of continuous cast steel being conveyed upon a line of rollers. This method comprises positioning against the bottom of the slab a dross removing blade having a flat top and a 90xc2x0 vertical end and then contacting the dross containing edges of the slab against the vertical end of the blade to cut the dross from the edges. This method further comprises positioning one or more vertical dross cutting blades with a flat top edge against the bottom of the slab for cutting the dross into smaller pieces.
A specific method of the invention uses two parallel, spaced apart, blade supports for removing dross from the bottom front and back edges of torch cut slabs of continuous cast steel being conveyed upon a line of rollers utilizing the apparatus described in the preferred embodiments, and comprising a sequence of the following steps:
positioning the apparatus to place the top blade support containing a pair of dross removing blades in the horizontal position;
passing in one direction a front edge of the slab beyond the apparatus;
rotating the apparatus so that the front edge of one of the dross removing blades is in horizontal contact with the bottom of the slab;
reversing the direction of the slab so that the dross contacts and is removed by the vertical end of the dross removing blade and clears the apparatus;
turning the apparatus at least 180xc2x0 from the original position and returning it to a horizontal position;
reversing the direction of the slab;
rotating the apparatus so that the front edge of a second dross removing blade is in horizontal contact with the bottom of the slab;
contacting and removing the dross from the back end, with the vertical end of the dross removing blade to provide a dross-free slab;
allowing the dross-free slab to continue past the apparatus on the line of rollers; and
turning the apparatus at least 180xc2x0 from the previous horizontal position.
The method further contemplates that the dross being removed by the dross removing blade is cut into sections by the dross cutting blade. Finally, the vertical disk is locked in the horizontal position between the dross removal steps.